MN-55 ELECTRON-SPIN ECHO ENDOR OF MN2+ COMPLEXES

The pulsed EPR technique of electron spin echo-electron nuclear double resonance (ESE-ENDOR) is used to measure Mn-55 nuclear spin transitions in a variety of orientationally disordered high-spin Mn2+ complexes. The large hyperfine interaction and the large net electronic spin of the S = 5/2 Mn2+ ion give rise to a number of interesting effects in the ENDOR spectrum. These are illustrated with ESE-ENDOR experiments on Mn2+ as a substitutional impurity in powdered SrO. The ''powder pattern'' Mn-55 ENDOR spectrum of Mn2+ present as an impurity in CaCO3 is more complicated due to the moderate zero field splitting interaction for the S = 5/2 ion in this matrix. The effects of substantial zero field splitting interactions are explored with Mn-55 ENDOR of Mn2+ in the protein concanavalin A and Mn2+ in a frozen water glass.